Add a stack of queues of elements with reaction queues.

Add a stack of queues of elements with reaction queues.

The ordering of custom element 'reactions' (various kinds of
callbacks) is determined by a stack which is pushed and popped within
the scope of an operation. The stack entry is a queue of involved
elements; this is so callbacks occur in order. However each element
gets callbacks in an internally consistent chronological order. To
effect this, each element has an associated reaction queue.

BUG=594918
Committed: https://crrev.com/e1a83859dd7df828f87fac61886f07f454dfffeb
Cr-Commit-Position: refs/heads/master@{#396806}

[dominicc (has gone to gerrit), 2016-05-31 02:16:12]

dominicc@chromium.org changed reviewers:
+ kojii@chromium.org

[dominicc (has gone to gerrit), 2016-05-31 02:16:13]

PTAL

Follow up from yesterday which uses the CustomElementReactionQueue.

[kojii, 2016-05-31 02:33:29]

lgtm

[dominicc (has gone to gerrit), 2016-05-31 06:07:16]

The CQ bit was checked by dominicc@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2016-05-31 06:07:33]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2027513002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/2027513002/20001

[dominicc (has gone to gerrit), 2016-05-31 07:12:43]

The CQ bit was unchecked by dominicc@chromium.org

[dominicc (has gone to gerrit), 2016-05-31 07:12:46]

The CQ bit was checked by dominicc@chromium.org

[dominicc (has gone to gerrit), 2016-05-31 07:12:46]

The patchset sent to the CQ was uploaded after l-g-t-m from kojii@chromium.org
Link to the patchset: https://codereview.chromium.org/2027513002/#ps20001
(title: "Rebase.")

[commit-bot: I haz the power, 2016-05-31 07:13:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2027513002/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/2027513002/20001

[commit-bot: I haz the power, 2016-05-31 09:14:28]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2016-05-31 09:16:50]

Description was changed from

==========
Add a stack of queues of elements with reaction queues.

The ordering of custom element 'reactions' (various kinds of
callbacks) is determined by a stack which is pushed and popped within
the scope of an operation. The stack entry is a queue of involved
elements; this is so callbacks occur in order. However each element
gets callbacks in an internally consistent chronological order. To
effect this, each element has an associated reaction queue.

BUG=594918
==========

to

==========
Add a stack of queues of elements with reaction queues.

The ordering of custom element 'reactions' (various kinds of
callbacks) is determined by a stack which is pushed and popped within
the scope of an operation. The stack entry is a queue of involved
elements; this is so callbacks occur in order. However each element
gets callbacks in an internally consistent chronological order. To
effect this, each element has an associated reaction queue.

BUG=594918

Committed: https://crrev.com/e1a83859dd7df828f87fac61886f07f454dfffeb
Cr-Commit-Position: refs/heads/master@{#396806}
==========

[commit-bot: I haz the power, 2016-05-31 09:16:51]

Patchset 2 (id:??) landed as
https://crrev.com/e1a83859dd7df828f87fac61886f07f454dfffeb
Cr-Commit-Position: refs/heads/master@{#396806}